Glazing with electrical terminal

ABSTRACT

A glazing provided with an electric circuit includes an electrically conducting substrate and a terminal for making electrical connection thereto. The terminal is attached to the glazing by an adhesive, rather than solely by solder, and the electrical connection between the terminal and the substrate is provided by means other than, or additional to, physical contact between the terminal and the substrate. For instance, the adhesive may be electrically conducting, or a soldered joint may additionally be provided if the adhesive is electrically insulating, or of insufficient conductivity for the type of circuit in question. The adhesive may be pre-applied to the terminal, and may be a tack-free adhesive activated or cured by heat. The terminal may be in two parts, with the base part of a standardized design. The glazing is suitable for use in buildings, appliances or vehicles, especially automotive vehicles.

DESCRIPTION

The present invention relates to a glazing provided with an electriccircuit including an electrically conducting substrate and a terminalfor making electrical connection thereto. In particular, the circuit maybe a heating element for defrosting or demisting the glazing, or anantenna circuit. The glazing may be for a vehicle window, or a windowfor an appliance or a building; in the case of a vehicle it may be awindscreen or rear window.

Various techniques are known for making electrical connection to aterminal. For instance, it is known from GB-A-2 223 385 to solder aterminal to a busbar or current collector. Alternatively, EP-A-410 766discloses an electrical device comprising a substrate supporting afilm-type heater track formed of conductive polymer ink. A connectormember is bonded to the substrate by means of adhesive, and the heatertrack overlies at least an end portion of the connector member toprovide an electrical contact between them.

It is also known from EP 278 611 A1 to employ an electrically conductiveadhesive to bond a busbar onto a conductive layer formed on a substrate,which may be used as a window. Furthermore, in GB 1 393 887, the use ofsteel filings to make electrical contact through an adhesive coating isdisclosed in the context of a rear window heating circuit.

However, FR 2 519 477 teaches that electrically conductive adhesiveshave various disadvantages, for example, they are not sufficientlydurable under the conditions to which a vehicle window is typicallysubjected, and they are expensive. Instead, FR 2 519 477 suggests thatit is preferable to employ a non-conductive adhesive to maintain asuitably configured terminal in intimate contact with an electricallyconducting substrate so as to ensure electrical continuity.

Unfortunately, the invention of FR 2 519 477 is also not withoutdisadvantages; it has been found that the inevitable mismatch of thethermal expansion coefficients of glass, metal and adhesive results in aweakening of the adhesive bond to the extent that electrical contact isadversely affected. Consequently, soldering remains a widely usedtechnique for attaching electrical terminals to glazings, although thestrength of the bonds produced is not always satisfactory, and there areincreasing environmental concerns about metals, such as lead, which arecommonly used in solders. Furthermore, the actual soldering operation isinclined to produce thermal stresses in the glass, which sometimes leadto damage.

It would be desirable to improve the attachment of electrical terminalsto glazings, avoiding the disadvantages described above.

According to the present invention there is provided a glazing with anelectric circuit including an electrically conducting substrate and aterminal for making electrical connection thereto, wherein the terminalis attached to the substrate by adhesive, characterised in that theelectrical connection between the terminal and the substrate is providedby means other than, or additional to, physical contact between theterminal and the substrate.

The provision of a secure and reliable electrical connection between theterminal and the substrate allows adhesives to replace solder withoutattendant problems of electrical continuity. Modern adhesives are ableto offer many advantages over solder. They may be flexible in the curedor set condition, and thereby absorb stresses generated in, or exertedon, the terminal. Adhesives are available which do not require to beheated in order to form a bond, or only need to be heated to a modesttemperature, and yet which still provide a strong bond. Furthermore, itis usually possible to arrange the manufacturing operation so that theadhesive is heated just before it contacts the glazing, thereby avoidingthe need to heat the glazing directly. Durable electrically conductingadhesives are now available, thereby allowing the adhesive to fulfilboth the mechanical and electrical functions of a conventional solderedjoint. Generally, such adhesives contain finely dispersed metal powderto make them conductive. Providing that the electric current to becarried is not large, the adhesive constitutes a sufficient electricalconnection. A further important advantage is that suitable adhesives areavailable which have fewer health and safety hazards and less adverseenvironmental impact than the conventionally used solders.

Preferably the terminal comprises separate base and connector partswhich are adapted to mutually engage, and the base part of the terminalis attached to the glazing by adhesive.

Advantageously, especially in the automotive industry, the base may beof a standardised design of general applicability, whereas the connectorpart may be tailored to the specific requirements of a particularglazing, vehicle or vehicle manufacturer. That is, the base ispreferably usable with a variety of differing designs of connector part.

Means of electrical connection between the terminal and the substratemay, for example, include the use of an electrically conductingadhesive, and/or a soldered connection. In high current applications, ajoint soldered directly between the terminal and the substrate ispreferable as the additional means of electrical connection, in order toobtain a low resistance connection. In this situation the soldercomplements the adhesive, as the latter bears the mechanical load andstresses, leaving the solder to provide, or enhance, electricalcontinuity without being compromised. This makes it possible, forinstance, to use solders which are less environmentally aggressive, evenif there is some loss in bond strength.

The invention also provides a method of making a glazing with anelectric circuit including an electrically conducting substrate and aterminal for making electrical connection thereto, comprising the stepsof:

providing a pane carrying the electric circuit and substrate, and

attaching the terminal to the substrate with adhesive, characterised by

providing the electrical connection between the terminal and thesubstrate by means other than or additional to, physical contact betweenthe terminal and the substrate.

Improvements can also be made in the type and method of application ofthe adhesive.

Preferably the adhesive is provided in the form of a tack-free tabletwhich is placed in contact with the terminal. The use of a tack-free(i.e. non-sticking) form of adhesive is advantageous because handling ofthe adhesive is greatly facilitated.

It is also preferable for the adhesive to be pre-shaped to match thepart of the terminal that the tablet is in contact with. This increasesthe area of the terminal that is bonded, and hence the strength of thebond, while reducing the likelihood of adhesive escaping from underneaththe terminal and becoming visible, which is likely to be unsightly. Italso results in less waste and hence a cost reduction.

Advantageously the adhesive is pre-applied to the terminal, e.g. theterminals may be supplied with adhesive already applied to the requisitepart of the terminal.

Optionally the adhesive may be heated to activate or cure it. The term“activating” an adhesive is used to refer to any process which initiatesthe bonding process, e.g. one which makes a previously tack-freeadhesive sticky, or one which starts the curing process. Activation mayinvolve melting the adhesive (at least on its surface), initiating aheat-dependent chemical reaction, or removing or destroying a barrierwhich separates two reactants. The extent of heating an adhesive isfrequently less than is required for solder, and with regard to heatingfor activation, the adhesive need not necessarily be in contact with theglazing at the time of heating.

In this specification, the 'term “solder” is used to denote a fusiblealloy of metals. The term “adhesive” is used to denote a substanceemployed to bond other substances together, but does not include asolder as such. An adhesive may be wholly non-metallic or may contain ametallic component.

The invention will now be further described by way of the followingspecific embodiments, which are given by way of illustration and not oflimitation, and with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of part of a glazing which includes anelectric circuit and has a terminal attached;

FIG. 2 is a perspective view of a terminal which comprises separate baseand connector portions;

FIG. 3 is a perspective view of a one-part terminal;

FIG. 4 is a plan view of the terminal of FIG. 3; and

FIGS. 5 (a)-(c) are perspective views of pre-shaped tablets of adhesive.

FIG. 1 illustrates a glazing 1 including an electric circuit 2. In thiscase the electric circuit is a resistive heating circuit printed on apane 3 of glazing material in a conductive ink. Such circuits are usedfor defrosting and demisting, e.g. in vehicles, and as they are wellknown they need not be described further. Other equally well-knownheating circuits comprise fine wires or a thin electroconductive coatingon the pane. Alternatively the circuit may be an antenna circuit, againas is well-known.

The pane 3 of glazing material may be a sheet of glass, which may beannealed or toughened, or a composite pane made up of two or more pliesof glass (or other glazing material) laminated together. In the case ofan automotive glazing, the glass would be safety glass, i.e. toughenedor laminated glass. There are alternative glazing materials to glassincluding various plastics such as polycarbonate for example.

Attached to the glazing, or more precisely, to an electricallyconducting substrate 4 which forms part of the-electric circuit 2, is aterminal 5. The embodiment of terminal 5 shown in FIG. 1 comprises abase part 6 and an upper (as illustrated) or connector part 7, which areadapted to mutually engage, as will be explained in more detail below inconnection with FIG. 2. The base part 6 is attached to the glazing 1 byadhesive 8, again as will be explained in more detail below. Theterminal may be in intimate physical contact with the substrate, butthis is not necessary since an alternative means of electricalconnection is provided, as described below.

In this embodiment, the electrically conducting substrate 4 constitutesa busbar supplying current to heating elements of the electric circuit2. The substrate may be composed of thin sheet metal, such as a foil, ormay be made from an ink which is applied to the pane (e.g. by screenprinting), dried, and fired to provide a durable conducting path. Forexample, silver-containing inks are widely used in the manufacture ofelectrically heated rear windows for vehicles.

The terminal 5 includes a spade connector 9, to which an electrical lead(not shown) may be attached in conventional fashion by a correspondingfemale connector. Many variations on the type and embodiment ofconnector are possible; for example, it may be cranked, or otherwisebent, to facilitate access or to improve its aesthetic aspect.Alternative forms of connector, e.g. the press stud type, may also beused. The terminal may be manufactured from thin sheet metal; inparticular, copper sheet, preferably tinned to prevent oxidation, is asuitable material.

FIG. 2 shows more details of the terminal 5. As already mentioned, theterminal 5 comprises a base part 6 and a connector part 7, which areadapted to mutually engage each other. For example, base part 6 may beprovided with tabs 20, which are bent around the connector part 7, e.g.around the spade 9.

It has already been mentioned that it is convenient for the terminals tobe supplied with the adhesive pre-applied, especially in a tack-freeform. The tablet of adhesive (generally comprising pre-mixed components)is pressed onto the surface of the terminal with just sufficient heat tocause it to adhere to the surface. When the terminal is in two (or moreparts) as in FIGS. 1 and 2, it is especially convenient for the basepart 6 to be of a standard universal design, with the adhesivepre-applied to it. This means that only one design of base part need bepurchased, which is then used with a connector part which suits theparticular vehicle glazing being manufactured. The base part may eitherbe attached to the glazing first, or to the connector first, whicheveris more convenient. In FIG. 2, a tablet of adhesive 8 is applied to theterminal base part 6, as indicated by arrow A. The base part is thenattached to the connector part 7 by means of tabs 20, as indicated byarrow B. Finally the terminal is attached to the glazing, as will bedescribed below.

The adhesive may be electrically conducting, in which case no furtherelectrical connection may be necessary. However, if the adhesive isnon-conducting, or if the electric circuit has a high power requirement,a means of electrical connection will be required between the terminaland the electric circuit. This may conveniently be provided by asoldered joint between the terminal and the electrically conductingsubstrate. In FIG. 2, the application of solder is diagrammaticallyrepresented by arrows C and solder 21. For an antenna, which of courseonly produces a very small current, the use of a conducting adhesive mayoften provide sufficient electrical connection.

FIG. 3 shows an alternative embodiment of terminal 30. This is aone-part terminal, i.e. it is a single piece, and it corresponds to theconnector part 7 of the terminal of the first embodiment. The terminalis attached to the glazing by means of adhesive 8; preferably a tabletof tack-free adhesive is used as described above. The tablet may beapplied to the terminal as indicated by arrow D. Again, an auxiliaryconnection may be made with solder 21.

FIG. 4 shows the one-part terminal 30 in plan view, with adhesive 8 andsolder 21 applied. It is advantageous for the tablet of adhesive to bepositioned near the base of the spade connector 40, where it can resistany bending moment created during application of a corresponding femaleconnector to the male spade 40, when the spade can act as a lever. Thesolder joint is thereby protected from damage.

FIGS. 5 (a)-(c) show shaped tablets 50, 51, 52 of adhesive, the tabletbeing pre-shaped to suit the shape of the terminal. Pre-shaping reduceswaste, improves conformity to the terminal surface and improves flowcontrol during application of adhesive. A stronger and neater bond isthereby obtained, and this technique may be used with either embodimentof terminal.

In FIG. 5(a), a T-shaped block 50 of adhesive is shown, which issuitable for use in the correspondingly T-shaped part of the terminal(i.e. where the limbs of the “T” cross, one limb being the spade). FIG.5(b) shows a thin rectangular block 51 of adhesive and FIG. 5(c) shows athin cylindrical tablet 52 of adhesive.

There are many suitable adhesives for attaching terminals to glazing.Polyurethanes are a suitable class of adhesives, includingmoisture-cured polyurethane (e.g. Betaseal HV3 available fromGurit-Essex AG of Freienbach, Germany), moisture/heat cured polyurethane(e.g. Sika 360 HC available from Sika AG of Switzerland), reactive hotmelt polyurethane (e. g, PUR-FECT 310 available from National Starch &Chemical Company of Bridgewater, N.J., USA, a member of the ICI Group),two component polyurethane, and other polyurethane-based compositions(such as Techbond PUR available from A. Raybond SARL of 68300Saint-Louis, France). A further suitable class of adhesives is that ofepoxy based compositions, e.g. Raybond's Techbond EPO. Also suitable arestructural adhesive tapes (e.g. 3M 9214 available from the MinnesotaMining and Manufacturing Company of St. Paul, Minn., USA). Suitableconducting adhesives contain finely dispersed metallic particles insufficient quantity to pass the required current density.

The preferred tack-free adhesives in tablet form are available from A.Raybond SARL in both epoxy and polyurethane compositions (Techbond EPOand PUR), and terminal base parts can be supplied with the adhesivepre-applied. In a polyurethane-based composition such as Techbond PUR,the polyol and isocyanate reactants are pre-mixed in stoichiometricratio, but the isocyanate is “end capped” or micro-encapsulated toprevent contact with the polyol. The adhesive is solid at roomtemperature. Application of heat activates the adhesive by destroying,e.g. melting, the capping or encapsulating membrane and allowing theisocyanate component into contact with the surrounding polyol so thatthe curing reaction starts. The method of use of these adhesives is asfollows.

A pane of glass carrying an electric circuit is provided and cleanedwith a cleaner such as Betaseal VP-04604 from Gurit-Essex; a terminal,or terminal base part, with tack-free adhesive pre-applied is alsoprovided. The terminal is positioned over the pane, and rapidly heatedto a temperature in the range 100°-140° C. Suitable rapid heatingtechniques include infra-red lamps, hot air jets, inductive heating orradio frequency dielectric heating. The heat activates the adhesive, andthe terminal is pressed into position on the pane. During the initialcooling period the terminal should be held in place, until thetemperature has reduced to a value in the region of 60°-80° C. The panemay then be moved, but the bond does not develop full strength untilpost polymerisation has been completed, which may require up to 20minutes at room temperature. Note that the pane need not be directlyheated, thereby reducing thermal stresses.

As mentioned above, in many cases it will be necessary to make aseparate electrical connection between the terminal and the circuit, anda preferred method involves soldering. In this case, the heat ofsoldering may advantageously also be used to activate the adhesive andeliminate a separate operation. The locations on the terminal body towhich solder is applied should be close to those to which adhesive isapplied. A soldering tool (which may be automated, e.g.robot-controlled) is then used to solder the terminal in position, andsimultaneously heat the adhesive to activate it. The soldering tool maybe one which contacts the work, or a hot air soldering technique may beused. Generally, soldering requires a higher temperature than activationof the adhesive, so the temperature attained may be governed bysoldering considerations. However, one of the advantages of theinvention is that the mechanical bond is provided by the adhesive, sothat the solder solely provides an electrical connection. Consequently,solders may be used which have a lower melting point than those used inthe prior art, where both mechanical and electrical considerationsapply.

In practice, certain types of adhesive are activated by melting them,and so the heat used to melt the solder preferably also melts theadhesive. It is therefore advantageous to select an adhesive and asolder which have similar melting points. Suitably, the adhesive andsolder have melting points within 20° C., preferably 10° C., mostpreferably 5° C. of each other.

What is claimed is:
 1. A glazing provided with an electric circuitincluding an electrically conducting substrate and a terminal for makingelectrical connection thereto, the glazing comprising a pane of sheetglazing material which carries the electric circuit, wherein theterminal is attached to the substrate by both adhesive and solder, suchthat the adhesive bears the mechanical load on the terminal and thesolder provides the electrical connection between the terminal and thesubstrate.
 2. A glazing as claimed in claim 1, wherein the terminalcomprises separate base and connector parts which are adapted tomutually engage, and the base part of the terminal is attached to thesubstrate by adhesive.
 3. A glazing as claimed in claim 1, wherein theadhesive is one which is activated or cured by heat.
 4. A glazing asclaimed in claim 1, wherein the adhesive is electrically conducting. 5.A glazing as claimed in claim 1, wherein the adhesive and solder havemelting points within 20° C., preferably 10° C., most preferably 5° C.of each other.
 6. A glazing as claimed in claim 1, wherein theelectrically conducting substrate is made from an ink which is appliedto the glazing, dried, and fired to provide a durable conducting path.7. A method of making a glazing provided with an electric circuitincluding an electrically conducting substrate and a terminal for makingelectrical connection thereto, comprising the steps of: providing a paneof sheet glazing material carrying the electric circuit and substrate,and attaching the terminal to the substrate with both adhesive andsolder, such that the adhesive bears the mechanical load on the terminaland the solder provides the electrical connection between the terminaland the substrate.
 8. A method as claimed in claim 7, wherein theadhesive is provided in the form of a tack-free tablet which is placedin contact with the terminal.
 9. A method as claimed in claim 8, whereinthe tablet is pre-shaped to match the part of the terminal that thetablet is in contact with.
 10. A method as claimed in claim 7, whereinthe adhesive is pre-applied to the terminal.
 11. A method as claimed inclaim 7, wherein the adhesive is heated to activate or cure it.
 12. Amethod as claimed in claim 7, wherein the heat of soldering alsoactivates or cures the adhesive.
 13. A method as claimed in claim 7,wherein the electrically conducting substrate is made from an ink whichis applied to the glazing, dried, and fired to provide a durableconducting path.
 14. A glazing as claimed in claim 2, wherein theadhesive is one which is activated or cured by heat.
 15. A glazing asclaimed in claim 2, wherein the adhesive is electrically conducting. 16.A glazing as claimed in claim 3, wherein the adhesive is electricallyconducting.
 17. A glazing as claimed in claim 2, wherein the adhesiveand solder have melting points within 20° C., preferably 10° C., mostpreferably 5° C. of each other.
 18. A glazing as claimed in claim 3,wherein the adhesive and solder have melting points within 20° C.,preferably 10° C., most preferably 5° C. of each other.
 19. A glazing asclaimed in claim 2, wherein the electrically conducting substrate ismade from an ink which is applied to the glazing, dried, and fired toprovide a durable conducting path.
 20. A glazing as claimed in claim 3,wherein the electrically conducting substrate is made from an ink whichis applied to the glazing, dried, and fired to provide a durableconducting path.